α-MoO3 with inhibitive properties in Fenton reactions and insights on its general impact on OH radical based advanced oxidation processes

Abstract

MoO3 is an intensively researched metal oxide, and it is considered a promising visible light driven photocatalyst and an excellent adsorbent of cationic dyes. In the present work orthorhombic α-MoO3 was obtained via calcination of ammonium heptamolybdate where structural modifications were induced by changing the applied calcination temperature (400–750 °C). Further subtle structural (crystallographic plane ratio) and morphological modifications were achieved via hydrothermal recrystallization. Differences between samples were clearly evidenced by various characterization techniques, especially in the case of the crystalline facet ratio and the morphology. The differently structured α-MoO3 samples were investigated as an inhibitor for Fenton reactions where the organic compounds decomposition relies on the generation of OH radicals. It was found that α-MoO3 strongly inhibits the rate of methyl orange (MO) decolorization. This might imply that MoO3 could be a OH radical scavenger since Fenton reactions’ effectivity relies on the presence of OH and O2– radicals. We demonstrated that the inhibition efficiency of α-MoO3 correlates strongly with the acidification rate of the aqueous solution in the presence of α-MoO3. However, this pH decline was consistent with crystalline facet ratio within a sample series, while the recrystallized samples disprove this structural connection showing a more complex relationship between the structural characteristics of α-MoO3 and its inhibitive properties of Fenton reactions. The present work pointed out that MoO3 can inhibit reactions which are based on intensive OH radical generation processes such as photocatalysis.